The present invention relates to an onboard road map display system for providing information on road map and traffic situations to a driver of a vehicle such as a motor vehicle.
Japanese Utility Model Provisional Publication No. (Hei)2-71877 shows a conventional road map display system which displays a map of roads by using a series of different graphic styles indicating possible vehicle speed levels determined by degrees of traffic congestion. In this conventional road map display system, however, roads in which traffic conditions are not monitored are not discriminated from monitored roads about which traffic information is available. A commonly assigned U.S. patent application Ser. No. 07/795,592 shows a similar navigation system having a road map display unit. This application is still pending and kept in confidence.